The public inquiry into the Stansted Airport expansion opened this morning as local and environmental groups took on the UK's largest airport owner.

A bank of protesters from around the country lobbied the opening day of the six-month hearing in Stansted.

Among the groups giving statements in the opening session are Friends of the Earth, Stop Stansted Expansion, and the National Trust. BAA, the Stansted owner, will also face the opposition of Stansted airlines easyJet and Ryanair, who want a less aggressive expansion.

Barry Stephens, 73, a retired oil industry professional from the nearby village of Stanbrook, said he was "not against flying" but objected to the proliferation of low-cost flights that has helped make Stansted the third largest airport in Britain.

If the expansion is approved, the passenger cap at the airport will rise from 25 million people per year to 35 million.

"I am a great believer in people being able to travel at reasonable costs," said Mr Stephens, standing outside the airport building that is hosting the inquiry. "And I am not trying to stop people travelling at a reasonable cost. But I find it absurd that these airlines are making money out of selling sandwiches and bottles of water, while charging inexpensive fares."

Sue Roderick, 61, a retired teacher from Thaxted, said: "North-west Essex is the only beautiful part of Essex. It is a beautiful place to live. We don't mind the airport per se; we just don't want it any bigger."

Local resident Suzanne Walker, 69, who attended with three generations of her family, including her four-month-old grandson, said: "We think the countryside is so valuable to everyone. We must take care of it."

Mrs Walker said she was attending to protest at the threat to Hatfield Forest, one of Europe's best-preserved medieval hunting forests. "It is of global importance because it is the only example left of its kind."

Anti-aviation campaigners also attended the hearing, which they have described as the biggest such inquiry concerning government policy since climate change became a major political issue. "If we can win this inquiry at Stansted, it will be a major reversal for the aviation industry and for the government's airport expansion plans," said John Stewart, chairman of Hacan, the campaign group fighting a third runway at Heathrow.

BAA, the UK's largest airport owner, made the opening statements in front of planning inspector Alan Boyland this morning. Representing BAA, Michael Humphries QC said Stansted was a "major piece of intrastructure" whose expansion is supported by government policy. He said Uttlesford District Council's rejection of the original planning application last year was a "direct challenge" to that policy.

Mr Humphries compared opposition to big infrastructure with the nimbyism of wanting central heating but objecting to power stations. "People expect their lights to come on when they turn the switch on the wall, but don't like living near power stations. They want their gas central heating to work in the winter, but do not like living near gas storage facilities."

Quoting extensively from the government's aviation policy as stated in a recent white paper, Mr Humphries added: "In a context where the government has decided, as a matter of national policy, that there is an 'urgent need for additional runway capacity in the south-east', it would be wholly irresponsible and, indeed, unsustainable not to make best use of existing runways in the south-east."

The Stop Stansted Expansion campaign and Uttlesford District Council will make their opening statements later today.